Sunday, October 12, 2014

Comparison between Three Phase Overhead and Underground cables

Power
can be transferred through Overhead cables or Underground cables. In overhead
lines inductance is predominant and in case of underground cables capacitance
is predominant.

There
are always advantages of Overhead transmission lines in comparison to
underground cables:-

1.The conductor used in Overhead transmission
lines is less expensive as size of cable required in overhead lines is less
than underground cables. As overhead lines have better heat dissipation than
underground cables.

2.Insulation cost in case of underground
cables is more than overhead lines. Overhead lines use bare conductors which
are well supported and provide sufficient spacing between conductors. But in
underground cables insulation is provided by various high grade paper tapes. A
metal sheath is also provided so that moisture doesn’t enter the cable. Oil and
inert gas is inserted so as to fill voids. Also storage vessels are needed to
be installed after some intervals so to makeup the voids created during
expansion and contraction of oil or gas in cables.

3.Also erection cost of overhead line is
much less than underground cables.

4.It is easy to do capacity addition in
overhead lines than underground cables.

There is some advantages of underground transmission than overhead transmission:-\